Windows on Arm64, x86/x64 emulation

[DavidXanatos]

hmpf... sooo I have a nice function hijacking code that from arm64 to arm64 works perfectly.

Now we also know that all processes in arm64 start execution as arm64 (or at least I think that) so at the very start of every program we should enter ntdll's LdrInitializeThunk and for arm64 on arm64 its of cause so.
For other architectures on arm64 we should at some point divert into emulated code.

When trying to inject a detour in LdrInitializeThunk of a created suspended x64 process on arm64 however that code does not seam to ever be executed. Meaning I can inject garbage and it will still startup just fine.

Now my assumption of how x64 on arm64 works is that as soon as execution goes into a system dll i.e. anything compiled as ARM64X we exit emulated x64 mode and execute the native arm code in the dll. So it stands to argue that wen bootstrapping a process, it behaves analogously everything is executed in native arm until it comes the time to call the x64 processes entry point.

Well it seams something isn't quite right here, one possibility is that the ARM64X dll's truly have all the code doubled including large portions of the arm code, so when I manipulate the LdrInitializeThunk I get i do it to a copy that will never be used.

Now I find that strange I would have assumed that the code wouldn't be doubled that MSFT would have some smart redirection in place allowing the ARM64X dll's to re use most of the arm code for the native and the emulated mode.

@RamMerLabs since you apparently have already a lot of experience with the layout of the new PE files, would you may be have a few tips is that really so that the code is fully separated?